Apparatus for producing uniform anolyte heads in the individual cells of a bipolar electrolyzer

ABSTRACT

A bipolar electrolyzer adapted for the electrolysis of aqueous solutions of alkali metal halides is disclosed. Also disclosed are methods of constructing and assembling the electrolyzer as well as modes of operation of the electrolyzer.

United States Patent [191 Raetzsch et al.

[ 4] APPARATUS FOR PRODUCING UNIFORM ANOLYTE HEADS IN THE INDIVIDUAL CELLS OF A BIPOLAR ELECTROLYZER [75] Inventors: Carl W. Raetzsch; Hugh Cunningham, both of Corpus Christi, Tex.

[73] Assignee: PPG Industries, Inc., Pittsburgh, Pa. [22] Filed: May 16, 1973 [21] Appl. No.: 361,014

Related US. Application Data [60] Division of Ser. No. 171,231, Aug, 12, 1971, Pat. No. 3,755,108, which is a continuation-in-part of Ser. No. 55,693, July 17, 19701 [52] US. Cl 204/255, 204/256, 204/257,

204/268, 204/269 [51] Int. Cl B0lk 3/10 [58] Field of Search 204/98, 255, 256, 257,

[ Dec. 24, 1974 [56] References Cited UNITED STATES PATENTS 2,219,342 10/1940 Stewart 204/256 2,543,059 2/1951 Rawles 1. 3,324,023 6/1967 Kircher 204/256 Primary Examiner-John H. Mack Assistant ExaminerW. 1. Solomon Attorney, Agent, or FirmRichard M. Goldman [57] ABSTRACT A bipolar electrolyzer adapted for the electrolysis of aqueous solutions of alkali metal halides is disclosed. Also disclosed are methods of constructing and assembling the electrolyzer as well as modes of operation of the electrolyzer.

2 Claims, 17 Drawing Figures PATENTED [153245174 SHEU 10F 9 PATENTEDUEEZMEM SHEET 5 0F 9 WMAWW F PATENTED 051241974 sum 8 or 9 IkH M lbl FIG. IO

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FIGJZ APPARATUS FOR PRODUCING UNIFORM ANOLYTE HEADS IN THE INDIVIDUAL CELLS OF A BIPOLAR ELECTROLYZER This is a division of U.S. application Ser. No. 171,231, filed Aug. 12, 1971, now U.S. Pat. No. 3,755,108, which is a continuation-in-part of U.S. application Ser. No. 55,693, filed July 17, 1970.

BACKGROUND OF THE INVENTION Aqueous solutions of alkali metal halides, as sodium chloride and potassium chloride, are electrolyzed to yield the alkali metal hydroxide, the halogen, and hydrogen. This electrolysis is generally carried out in one of two types of cells-the mercury cell and the diaphragm cell.

In the diaphragm cell there are two electrolyte compartments. One is the cathode electrolyte compartment or catholyte compartment. The other compartment is the anode electrolyte compartment or anolyte com partment. These two compartments are separated by a semi-permeable diaphragm, typically of asbestos.

Diaphragm cells may be electrically connected in series in a common housing with the anodes of one diaphragm cell being electrically in series with the cathodes of the prior cell in the circuit and mounted on the opposite side of a common structural member (e.g., a backplate) therewith, and the cathodes of the cell being in series with the anodes of the next adjacent cell in the circuit and mounted on a common structural member. Such a configuration is called a bipolar configuration. An assembly of diaphragm cells in bipolar configuration, the anode of one cell being electrically in series with and physically connected to the cathode of the next adjacent cell by means of a common structural member within the electrolyzer, is called an electrolyzer.

The common member, having a backplate with both the anodes of one cell and the cathodes of the next adjacent cell in the series connected thereto, is called a bipolar unit."

The assembly provided by the anodes of one bipolar unit interleaved with the cathodes of the adjacent bipolar unit and facing each other so that electrolysis of alkali metal chloride solutions surrounding these anodes and cathodes may be carried out therebetween, is called a bipolar cell."

Bipolar electrolyzers are described in Mantel], Electrochemical Engineering, (4th Ed.), McGraw-Hill Book Co., Inc., New York, N.Y. (1969), and in Kircher, Electrolysis of Brines in Diaphragm Cells in Sconce, Chlorine, Reinhold Publishing Corp., New York, N.Y. (1962). Bipolar electrolyzers of the prior art are shown in U.S. Pat. No. 1,907,818 to R. M. Hunter, U.S. Pat. No. 2,161,166 to R. M. Hunter, U.S. Pat. No. 2,282,058 to R. M. Hunter, U.S. Pat. No. 2,858,263 to I. L. Lucas, et al., and U.S. Pat. No. 3,337,443 to Raetzsch, et al.

SUMMARY OF INVENTION In order to take advantage of the apparent economies of bipolar electrolyzers, a plurality of individual bipolar units should be present in one electrolyzer. Additionally, electrolysis should take place at high anode current densities, high currents, and high brine feed rates. Furthermore, the time lost for maintenance and repairs, as well as the cost of maintenance and repairs, should be minimized.

Economies of operation may be obtained by operating at high anode current densities; for example, above about Amperes per square foot of anodic surface. Additionally, the current per square foot of backplate area should be high, typically above about 1,250 Amperes per square foot of backplate.

Economies may also be obtained by minimizing electrolyte seepage into the backplate. This may be accomplished by providing a backplate having substantially continuous anodic and cathodic surfaces, that is, anodicand cathodic surfaces that do not have any breaks, breaches, or discontinuities. In such a backplate separate electrically-conductive structures breaching the backplate to provide both mechanical and electrical connection between the anodes and the cathodes are eliminated. In a bipolar unit having such a backplate, the backplate itself becomes the electricallyconductive structure, and means are provided to minimize the electrical resistance between the anodes and cathodes connected thereto.

DETAILED DESCRIPTION OF THE INVENTION In the drawings:

FIG. 1 is an exploded view showing the general arrangement of the interior of an electrolyzer.

FIG. 2 is a partial cut-away side elevation of an electrolyzer.

FIG. 3 is a partial cut-away front elevation of an electrolyzer.

FIG. 4 is a partial cut-away plan. view of an electrolyzer.

FIG. 5 is an exploded partial cut-away of an individ ual bipolar unit.

FIG. 6 is a cut-away drawing of a bipolar cell within the electrolyzer taken along plane VI-VI of FIG. 1.

FIG. 6A is an enlarged view of a portion of FIG. 6 showing the interface between an anode base and an anode bar.

FIG. 6B is an enlarged view of a portion of FIG. 6 showing the interface between an anode bar and the anodic surface of the backplate.

FIG. 6C is an enlarged view of a portion of FIG. 6 showing the interface between the backplate and the copper sheet.

FIG. 7 is a cut-away drawing of a cathode.

FIG. 8 is one form of an anode that may be used in the electrolyzer of this invention.

FIG. 9 is another form of an anode that may be used in the electrolyzer of this invention.

FIG. 10 is a side elevation of the supporting structure of the electrolyzer.

FIG. 11 is a plan view of the supporting structure shown in FIG. 10.

FIG. 12 shows the apparatus used in assembling the electrolyzer.

FIG. 13 is a view of the compression means of sealing the electrolyzer taken along plane XIII-X111 of FIG. 2

FIG. 14 is a perspective, schematic view of the electrolyzer showing the equalizer and the individual cells.

An arrangement of bipolar units forming an electrical series of bipolar cells in an electrolyzer is shown in exploded cut-away in FIG. 1 and in partial cut-away in FIGS. 2, 3, and 4. Bipolar units 11, 12, 13, and 14 form bipolar cells 16, 17, and 18. End unit 11 provides a cathodic half cell, while end unit 14 provides an anodic half cell. The intermediate bipolar units 12 and 13 are bipolar units providing both anodic and cathodic half cells.

In addition to the end half units 11 and 14, an electrolyzer will normally include at least one bipolar unit 12 and may be comprised of a plurality (up to 11), or 15, or even more) of bipolar units 12 and 13. Thus, while only two intermediate units are shown in the figures, bipolar diaphragm electrolyzers with any number of bipolar units are included within the contemplation of this invention, the number of such units being theoretically unlimited and, in fact, being limited only by economic considerations.

The anodes 31 of one bipolar unit 13 are interleaved with and parallel to the cathodes 41 of the adjacent bipolar unit 12. The electrodes are substantially parallel to the side walls 122 and 123 of the electrolyzer, and substantially perpendicular to the top 121 and bottom 124 of the electrolyzer, and to the backplates 21 of the individual bipolar units 11, 12, 13, and 14.

Within such a bipolar cell 17, assembled as described, the electrical current flows from the backplate 21 of bipolar unit 13, along the anode 31 attached thereto, in a direction substantially perpendicular to the backplate. The electrical current then flows from the anode 31, to the cathode 41 through the electrolyte, in a direction substantially perpendicular to the electrodes 31 and 41. Finally, the electrical current flows along the cathodes 41 to the backplate 21 of the next bipolar unit 12.

Within such a cell an anode 31 is spaced substantially equidistant from both of the cathodes 41 between which it is interleaved whereby substantially equal inter-electrode gaps are provided. In this way the IR voltage drops for the current flowing from either surface of the anode 31 are substantially equal. The interelectrode gap, that is, the distance measured perpendicular to the electrodes between the anode 31 and the opposite cathode 41, is from about A inch to about /4 inch, and is typically /2 inch. The interelectrode gap should be narrow enough to minimize the IR voltage drop across the electrolyte between the anode and the adjacent cathode and thereby minimize the resistance heating of the electrolyte. The inter-electrode gaps should, however, be great enough to prevent abrasion or washing off of the diaphragm 101 by the chlorine liberated at the anodes 31.

The pitch of the electrodes, that is, the center-tocenter distance between electrodes of like polarity measured parallel to the top 121, bottom 124, and backplate 21 of the bipolar unit, and perpendicular to the plane of the electrodes, is numerically equal to the sum of the thicknesses of one anode and one cathode plus two times the inter-electrode gap. As the pitch of the electrodes is reduced, the number of electrodes per foot of backplate width is increased. In this way, increased current capacity and, therefore, increased chlorine production capacity is provided without increasing either the anode current density or the width of the electrolyzer.

Anodes used in the electrolyzer of this invention are sheet like and made of materials which render them dimensionally stable. That is, they comprise a valve metal having an electroconductive surface thereon. Such dimensionally stable anodes are less than /2 inch in thickness; typically they have a thickness of from about l/32 inch to about Va inch. This compares with an anode thickness of from about 1 inch to about 1 /4 inches for the carbon anodes used in bipolar electrolyzers of the prior art, exemplified by U.S. Pat. No. 3,337,443 to Raetzsch, et al. The use of dimensionally stable anodes allows the pitch of the electrodes to be reduced by about 1 inch from the pitch of the electrodes in an electrolyzer having graphite electrodes and results in a pitch of about 1% inches to about 2% inches.

As described above, an electrolyzer is comprised of a plurality of bipolar units. A bipolar unit 12 used in the electrolyzer of this invention is shown in exploded view in FIG. 5 and in cut-away view along plane VIVI of FIG. 5 in FIG. 6.

The backplate 21 serves as the partition between the bipolar cells 16 and 17 and as the electrical conductor between the anodes 31 of bipolar cell 16 and the cathodes 41 of bipolar cell 17.

Backplate 21 of bipolar unit 12 comprises a valve metal sheet 22 on the anodic side of the unit 12 and the cathodic metal plate 23 on the cathodic side of the unit 12. The valve metal sheet 22 and the cathodic metal plate 23 are joined together to provide the backplate 21. Sheet 22 and plate 23 may be joined by explosive bonding, as described in U.S. Pat. No. 3,137,937 to Cowan, et al., by welding with a suitable intermediate, by soldering with suitable soldering fluxes, or by mechanical means such as clamping or bolting. However, in order to minimize the voltage drop across the backplate 21, unless direct electrical connection is provided between the anodes 31 and cathodes 41, as by copper studs, it is particularly important that the contact between the anodic sheet 22 and the cathodic plate 23 be intimate contact. The service life of the backplate 21 may be increased by providing substantially continuous anodic and cathodic surfaces, that is by avoiding any breaches of either the anodic sheet 22 or the cathodic plate 23 on any part of the backplate that is subjected to the electrolyte.

The cathodic plate 23 may be iron, steel, or stainless steel. It may contain carbon and alloying elements as molybdenum, chromium, nickel, cobalt, silicon, vanadium, titanium, zirconium, or niobium. Alternatively, the cathodic plate may be copper plate or any plate resistant to the catholyte. As a matter of terminology, whenever the term steel" is used herein, it will be understood to include iron and alloys of iron.

The valve metal sheet 22 is fabricated from a metal that forms a protective oxide coating conductive only in the cathodic direction, whereby it is immune from attack by the anolyte. Valve metals include titanium, tantalum, and tungsten. For economic reasons titanium is more frequently used. It will be understood that although reference is usually made herein to sheets of titanium, sheets of other valve metals are also intended.

In electrolyzers of this invention a copper sheet 24 is attached to the steel surface 23 of backplate 21. The copper sheet serves to suppress the migration of atomic hydrogen through the steel plate 23 to the interface between the steel plate 23 and the titanium sheet 22 during electrolysis.

Commonly assigned, copending application U.S. Ser. No. 158695 now U.S. Pat. No. 3,759,183 of Raetzsch, et al., re ELECTROLYTIC CELL a continuation-inpart of U.S. application Ser. No. 55,693, now abandoned describes a plurality of expedients for coping with this hydrogen situation. Thus, it discloses that this copper sheet 24 may be in contact with but not bonded to the steel plate 23 and, preferably, will be spaced at least 5 Angstroms from steel plate 23, thereby facilitating the combination of atomic hydrogen to molecular hydrogen. And, as further described in the above application, an iron or steel sheet may be substituted for the copper sheet. Alternatively, a protective layer may be applied to the iron plate 23 as described in copending application U.S. Ser. No. 158,695, now US. Pat. No. 3,759,813 of Raetzsch, et al., re ELECTROLYTIC CELL a continuation-in-part of US. application Ser. No. 55,693, now abandoned. This layer may have either hydrogen barrier properties, or high hydrogen overvoltage properties (relative to the cathodes 41 or both. Whenever a copper sheet is referred to in this specification, it will be understood that other protective measures may also be used, as an iron or steel sheet or a hydrogen barrier metal coating.

The copper sheet 24 is from about l/32 inch to about /1 inch thick. In order to prevent the formation of interstitial water within the copper sheet 24, the copper used therein should have a low oxygen content. Best results are obtained if the copper sheet 24 is fabricated from oxygen free high conductivity coppers, such as sold under the trademark OFI-IC.

The copper sheet 24 isolates the cathodic surface of the steel plate 23 from contact with the catholyte. Various methods of supporting sheet 24 may be used. As shown in FIG. 6C, a space 51 of more than about 5 Angstroms is provided between the steel plate 23 and the copper sheet 24. This space allows any atomic hydrogen diffusing through the copper sheet 24 during electrolysis to recombine into molecular hydrogen be fore reaching the steel plate 23. As shown in FIG. 6C, the space 51 between the steel plate 23 and the copper plate 24 is vented through vent 52.

On the surface of the copper plate 24 are copper studs 61. These studs 61 do not breach steel plate 23. They are welded to the steel plate 23 in vertical and horizontal array. The studs are plug welded to plate 23 through opening 65, the plug weld providing electrical contact between stud 61 and iron plate 23 and holding copper sheet 24 against iron plate 23. In this way, the cathodes 41 are mechanically and electrically connected to the backplate 21 without breaking steel plate 23, thereby providing a substantially continuous cathodic surface and minimizing the possibility of catholyte seepage into the backplate. Each stud may carry from 1,000 to 2,000 Amperes from the cathodes 41 to the backplate 21. The studs 61 may be circular and may have vent holes 63 therein. If vent holes 63 are provided, they may comprise about 5 per cent of the total volume of stud 61.

Welded to copper stud 61 in the assembled bipolar unit 12 is copper stud 67. Copper stud 67 is a cylinder wherein surfaces 69 and 71 may be recessed from the leading edge 73 of stud 67. Offset from the central axis of stud 67 may be vent hole 75. While it is preferred in the welding of stud 61 to stud 67 to align vent hole 63 with vent hole 75, this is not essential as the hydrogen flowing through vent hole 75 will flow into the compartment 76 defined by the recessed surface 71, and leading edge 73 of stud 67 and the surface of stud 61. From compartment 76 the hydrogen will flow through vent hole 63. From vent hole 63 the molecular hydrogen will diffuse through vent 51.

Welded to the front of studs 67 and electrically connected thereto are steel bars 80, as illustrated in FIGS. 1, 2, 3, 4, 5, and 6.

A plurality of steel bars are joined to the copper sheet 24. Steel bar 80 has studs 67 welded to one face thereof. Welded to the opposite face of the steel bar 80 are the cathodes 41.

The cathodes 41 are shown generally in FIGS. 1, 2, 3, 4, 5, and 6, and with particular detail in FIG. 7. The cathodes 41 have two faces 42 and 43 and are joined together at the top 44, bottom 45, and edge 46 opposite the backplate. The cathodes are typically of wire mesh screen. The mesh must be large enough to present a large fraction of open area for unimpeded migration of the alkali metal ions, but small enough to be impervious to the diaphragm during assembly. The wire mesh may be of any electroconductive metal suitable for use in a cathodic environment. A suitable cathode material 6 by 6 mesh 3/16 inch doubled, crimped 0.092 inch diameter steel screen. The cathodes typically have an over-all width of from about /2 inch to about inch, with an interior width typically of from about Vi inch to about inch. The interior width of the cathodes must be such as to allow for the movement of the catholyte and catholyte gases substantially without frothing or entrainment.

In fabricating the cathodes, one sheet of screen is used for each cathode. This sheet of screen is folded in half thereby forming the leading edge 46 of the cathode. The top 44 and bottom edges 45 are welded together, resulting in wire-to-wire joints.

Steel plugs 47 are spaced at intervals along the heighth of the cathode between the two sides 42 and 43. These plugs 47 are welded to the sides 42 and 43.

They provide added rigidity to the cathodes and pre-.

vent the collapse of the cathodes while pulling the dia phragm.

At the open edge 48 of the cathode 41 are a plurality of steel fittings 49. These fittings are welded to the sides 42 and 43 of the cathode. In turn, these fittings 49 are welded to the steel cathode bars 81), thereby providing physical and electrical connection between the cathode fingers 41 and the backplate 21.

The cathode backscreen 86 is shown generally in FIGS. 1, 2, 3, and 4, and with particular detail in FIGS. 5 and 6. The backscreen comprises a plurality of backscreen elements 86a, 86b, and 86c for example. These elements fit against the cathode fingers 41 and against the cathode conductor bars 80.

An asbestos or permionic diaphragm 101, shown generally in FIGS. 2, 3, and 4 and in more detail in FIG. 6, is applied to the mesh components as the cathode fingers 41, the backscreen 86 and. the diaphragm are typically from l/l6 inch to 3/16 inch thick. The compartment within the diaphragm 101, provided by the backplate 21, the anode fingers 41, and the backscreen 86, is the catholyte compartment.

Turning to the anodic side of the bipolar unit 12, the titanium sheet 22 faces the anolyte. Connected to the titanium sheet 22, typically by welding, are a plurality of titanium bars 32 shown generally in FIGS. 1, 2, 3, and 4 and in further detail in FIG. 6. The anodes, shown generally in FIGS. 1, 2, 3, 4, and 5, are bolted to the bars 32 rather than being bolted directly to the backplate. This avoids breaching the anodic sheet 22 and provides a substantially continuous titanium sheet, thereby minimizing the possibility of anolyte seepage into the backplate.

The anode bars 32 may be fabricated of titanium or of any valve metal. Alternatively, the anode bars may be fabricated of copper or any similarly conductive metal and clad with a valve metal. Alternatively, studs may be substituted for the bars 32.

Electrical current flows from the valve metal sheet 22 of the backplate 21 to the anode bar 32 across the interface therebetween. The electrical current then flows from the anode bar 32 to the base 36 of the anode across the interface therebetween. Each of the interfaces gives rise to a contact resistance.

Under vigorous conditions of electrolysis, for extended periods of time, the contact resistance can increase. This increase in contact resistance is characterized by the formation of valve metal oxides at the interfaces.

Both the initial contact resistance and the increase of contact resistance with time may be substantially reduced by providing, at the points of electrical contact within the interfaces, electroconductive coatings resistant to oxidation under anodic conditions. In one exemplification, suitable electroconductive coatings are provided by platinizing each surface of the pair of surfaces in contact with each other. In this way platinumplatinum contact 30 is provided between the base 36 of the anode 31 and the anode bar 32 as shown in FIG. 6A.

In one exemplification the anode base 36 is connected to the anode bar 32 by means of a bolt 29 and a washer 28. The bolt 29 is typically shorter than the thickness of the anode bar 32 so that the bolt 29 does not breach the valve metal surface 22 of the backplate 21. Typically the bolt 29 and washer 28 are fabricated of the same material as the anode bar 32.

The anodes are shown generally in FIGS. 1, 2, 3, 4, 5, and 6, and in detail in FIGS. 8 and 9. Each anodic element is interleaved between a pair of cathodes as previously described and may have one blade, as shown in FIG. 8, or two blades, as shown in FIG. 9. For most efficient operation, the anode blades 33 should be substantially parallel to the cathode fingers 41. The anode blades may be substantially perpendicular to the backplate if the cathode fingers are straight; or, if the cathode fingers are tapered, the anode blades are parallel to the tapered cathode fingers, thereby forming an acute angle with the backplate.

As described previously, the anode blades may be in the form of a plate or a perforate sheet and are typically from about 1/32 inch thick to about As inch thick.

The anode blades may be fabricated of any metal that, when subjected to an anodic medium, forms a protective oxide film conductive in the cathodic direction. Such metals are known as valve metals and include titanium, tantalum, and tungsten. Typically, for reasons of cost and availability, titanium is used. Whenever titanium is referred to, it will be understood that any of the valve metals are interchangeable with it and can be used in its place. An electroconductive surface is applied to the anode blades. The electroconductive surface typically comprises a platinum group metal or metal oxide.

In one exemplification shown generally in FIGS. 1, 2, 3, 4, 5, and 6, and in detail in FIG. 8, the anodes comprise a metal blade 33 having surfaces 34 and 35 and a base 36 for attaching the anode to the anode bar 32. In the exemplification shown in FIG. 8, electroconductive surfaces may be provided on one or both faces 34 and 35 of the anode. Alternatively, the anodic element may be in the form of two perforate or foraminous sheets, as shown in FIG. 9, and may be interposed between a pair of cathodes. In the exemplification shown in FIG. 9, either the pair of faces within the anodic element 34a and 34b or the pair of faces facing the cathodes 35a and 35b, or both pairs of faces may be provided with an electroconductive surface. Typically, only the interior pair of faces 34a and 34b will be provided with an electroconductive surface thereby reducing the abrasive effects of the evolved chlorine on the diaphragm and allowing a reduced interelectrode gap.

The volume provided by the diaphragm 101 of one bipolar unit and the anodic surface 22 of the next bi polar unit and containing the anodes of that next unit is the anolyte compartment. The anodes 31 and cathodes 41 are of substantially equal length (i.e., measured from backplate to backplate). The length is determined by optimization methods and is generally from 1 to 2V2 feet.

Each of the bipolar units, as bipolar unit 12, is housed in a channel frame 110. The channel frame is shown generally in FIGS. 2, 3, and 4 and in particular detail in FIG. 5. The channel frame 110 comprises sidewalls 122 and 123, top 121, and bottom 124. Each wall, as walls 122 and 123, top 121, and bottom 124, has a pair offlanges 126 and 127. Flange 126 is bolted to the cathodic surface 24 of backplate 21 by bolts 129 and insulated from backplate 21 by gasket 139. Flange 127 is separated from the backplate of the next adjacent unit by flange 140.

Wall 133 forms an acute angle with the bottom 124. The volume 115, provided by wall 133 and segments of the bottom 124 and side walls 122 and 123, communicates through wire mesh side channel 87 with the catholyte volume 103. Opening 116 in side wall 123 is used to drain compartment and thereby recover catholyte from volumes 102 and 103.

Wall 135 forms an acute angle with the top 121. The volume 111, provided by wall 135 and segments of the top 121 and side walls 122 and 123, communicates through wire mesh side channel 87 with catholyte volume 103 and collects gaseous cathode products as H The outlet 112 in top wall 121, leading from volume 111, is used to remove gaseous cathodic products.

Openings 117, 118, and 119 in side walls 122 and 123 and the top 121, respectively, lead into the anolyte compartment. Opening 119 may be used to remove gaseous anolyte porducts, as chlorine. Opening 117 is used to feed brine into the anolyte compartment.

Channel frame 110 may be fabricated from iron, steel, titanium, titanium-clad steel, or rubber-lined steel. Most commonly, steel is used. Those portions of walls 121, 122, 123, 124, 133, and 135 in contact with the anolyte should be protected against corrosion. Suitable linings 125 include rubber, plastic, ebonite, and titanium. Most commonly, rubber or titanium is used.

The individual bipolar units 12 including electrodes 31 and 41, backplate 21, and channel frame 110 weight upward of 1V2 tons and may weigh over 3 tons, depending upon the current capacity and brine capacity.

The electrolyzer itself rests on a base frame shown in FIGS. 10 and 11. The base frame comprises rails 161a and 161b, each rail having an insulating layer 162 thereon. The insulating layer may be shale, concrete, or plastic. The base frame itself is insulated from the cell room floor by insulators 163 (as shown in FIG. 2).

, As shown in FIG. 12, the electrolyzer is assembled by first installing the winch 171 on winch base frame 172. Winch 171, having handles 173, a center member 174, wire take-up means 175 and 176, and mounted on base frame 172, is installed on end plates 164 of the base frame 160. The individual bipolar units are then mounted on the insulating layers 162 of the base frame 160. The cathodic end unit 11 is mounted first. The intermediate bipolar units 12 and 13 are then mounted such that the anodes of one unit may be interleaved with the cathodes of the next adjacent bipolar unit in the electrolyzer. Finally, the anodic end unit 14 is mounted on the base frame 163. Alternatively, the order of installing the bipolar units may be reversed, with the anodic end unit 14 being installed first, then the intermediate bipolar units 12 and 13, and finally the cathodic end unit 11.

Oneach side of the electrolyzer a metal line or wire 178 is run from the winch take-up means 175 through lugs 130 in the side walls of each unit to a hook eye 180 which connects, through lug 130, with a wing nut or throttling nut 182 and a stay 184.

A pair of temporary guide frames 191 shown in FIGS. 3 and 12 are installed in notches 192 in the bottom 124 of the channel frames 110, thereby more accurately p sitioning the individual units 12 and 13 on the base frame 160. The individual bipolar units 11, l2, l3, and 14 are then slowly winched together along the insulating layer 162. Alternatively, each bipolar unit may be individually winched along the insulating layer 162.

The total assembly of individual units comprising the electrolyzer is held together by providing a compressive force on the two end half units. Specifically, a plurality of tie rods 186 shown generally in FIGS. 2, 3, and 4, and in greater detail in FIG. 13 apply a compressive force on the two end half units 11 and 14.

Each tie rod 186, enclosed in an insulating sleeve 187, passes through lugs 130 welded to the walls of the channel frame 110 of the end half units 11 and 14. An insulating washer 188 and insulating cap 189 electrically insulate the lugs 130 from the nuts 190. The nuts 190 provide the compressive force.

In the operation of the electrolyzer brine containing from about 310 gpl to about 325 gpl of sodium chloride is fed through the feed line 155. This feed mixes with chlorinated brine from tank 151 yielding a chlorinated brine containing from about 250 grams per liter to about 290 grams per liter of sodium chloride which is fed into the anolyte compartment through the brine inlet 117 at the side of the anolyte compartment. The following reaction takes place at the anodes in the anolyte compartment: Cl" fiaCl e The chlorine liberated at the anode 31 bubbles up on the face of the anode 33 through the anolyte to the top of the anolyte compartment and thence out of the cell through the chlorine outlet 119 and through brine feed tank 151. The electrolyte permeates the diaphragm 101 and passes through it into the catholyte compartment. The following reaction takes place at the electrically active surfaces within the catholyte compartment: Me H O e MeOI-I /2Hz The hydrogen gas bubbles up and back through the catholyte compartment 102 of FIG. 6 into the catholyte backscreen compartment 103 of FIG. 6 and into compartment 111 of FIGS. 2 and 5, and finally out through the hydrogen outlet 112 into pipe 113 shown in FIGS. 2, 4, and in the top of the bipolar unit. The cell liquor containing from about to about grams per liter of sodium hydroxide and about 140 to about 170 grams per liter of sodium chloride is recovered from the catholyte compartment through opening 116 in wall 122 and discharged through the perc pipe 120. The perc pipe 120 is rotatably mounted on pipe 114 leading from opening 116. Rotating the perc pipe 120 changes the hydrostatic pressure in the catholyte compartment, thereby changing the difference between the catholyte hydrostatic pressure and the anolyte hydrostatic pressure. In this way, as the permeability of the diaphragm decreases with service, the catholyte hydrostatic pressure may be made significantly less than the anolyte hydrostatic pressure thereby causing electrolyte to flow through the diaphragm.

In order to obtain economical operation of the electroylzer, the inter-electrode gap should remain uniform along the length of the anode. Accordingly, means are provided to keep the anode blades in proper alignment with each other and with the cathode fingers and to ad justably maintain the proper inter-electrode gap and anode pitch. In one exemplification of this invention shown in FIGS. 2, 3, 4, 8, and 9, this takes the form of a threaded rod 38 passing laterally across and substan' tially perpendicular to the anode blades in a direction substantially parallel to the top 12 and bottom 124 and to the backplate 21, and substantially perpendicular to and through fittings 37 on the top and bottom of each anode 31. These fittings may be only at the top of the blades or only at the bottom of the anode blades or at both the top and bottom of the anode blades. Nuts 40 and washers 39 are on the threaded rod 38 on both sides of the fitting 37. Adjustment of the nuts 40 maintains the pitch of the anode blades. In another exemplification where the anodes are longer in the vertical direction than the cathodes, a notch can be provided in an edge of the blades of the anodes themselves. The rod then goes through the notches in the edge of the anode blades and laterally to the blades, across the cell, from wall 122 to wall 123. The notch or opening, which may be near the upper horizontal edge of the anode blade or near the lower horizontal edge of' the anode blade or there may be openings near both edges, is of sufficient diameter to allow the rod 38 to pass through, but of a sufficiently small diameter that the nuts 40 will maintain the blade in the desired position.

In the normal operation of the electrolyzer, brine attack fed into the anolyte compartment through a pipe 153 shown in FIGS. 3 and 4 to an opening 117 in the side wall 122 of the bipolar unit and through openings 119 in the top 121 of the bipolar unit. I-Ioweveryshould the flow of brine to any cell in the electrolyzer be interrupted, the anolyte level could drop. This could cause abnormalities in the operation of the individual cell such as the anodes being exposed to the air, hydrogen entering the anolyte compartment, boiling of the anolyte, electrolytic attach of the backplate or anodes, or arcing across the electrodes. Any of these abnormalities could result in catastrophic failure of the electrolyzer. Accordingly, an equalizer 157 is provided. The equalizer, shown generally in FIGS. .3 and 4, and specifically in FIG. 14, serves to maintain a uniform head of anolyte in all of the individual cells. This is accomplished by providing hydraulic communication between a plurality of the individual cells in the electrolyzer. This hydraulic communication may be provided by an equalizer pipe or equalizer pipes, as 157 in FIGS.

3, 4, and 14, connecting the individual cells 16, 17, and 18 through openings 118 in the walls 122 of the cells. In the arrangement shown in FIGS. 3, 4, and 14, the brine moves as shown by the arrows in FIG. 14 to overcome hydrostatic irregularities. Typically, the equalizer is external of the individual cells and the electrolyzer in order to provide a longer distance of electrolyte between cells, thereby minimizing current leakage. The resistance across the equalizer between adjacent cells in the electrolyzer is from to 100 ohms, and preferably from 50 to 100 ohms. Alternatively, or additionally, the brine feed pipes 153 of the individual cells may be interconnected.

All of the cells 16, 17, 18, in the electrolyzer may be in hydraulic communication with each other. Alternatively, only a number of cells-the number being less than the total number of cells in the electrolyzer-may be in hydraulic communication, through one equalizer 157, in which case a plurality of equalizer pipes 157 will be provided. The cells connected to any one equalizer 157 may be adjacent or they may be non-adjacent cells separated by cells connected to other equalizers 157.

In still another exemplification where a plurality of brine header pipes are provided (each of the brine header pipes feeding a plurality of adjacent cells), a plurality of equalizer pipes may be provided. In this case, each equalizer 157 may hydraulically connect cells receiving brine from a different header. In this exemplification, the deleterious effects of an interruption of brine feed occurring in the brine header can be minimized.

The openings 118 in the walls 122 through which hydraulic communication is provided should be below the level of the anolyte and the tops of the cathodes. The openings 118, however, may either be in line or horizontally offset one from the other. Accordingly, the equalizer pipe 157 may be horizontal or it may be offset from the horizontal.

The equalizer is hydraulically responsive to changes in the electrolyte level within the cells with which it communicates. As the hydrostatic pressure, or head, within one of the individual cells starts to fall, electrolyte will flow out of the other cells in hydraulic communication therewith, through the equalizer pipe 157, to the said cell. In this way the hydrostatic pressure across a plurality of cells in hydraulic communication is maintained substantially uniform, and individual hydrostatic variations over time within a cell are substantially reduced.

The brine tank 151, the equalizer pipe 157, and the brine feed pipe 153 are steel and are lined with a material suitably resistant to saturated brine. Rubber, polyester, and plexiglass may be used. Typically, polyester is used. The equalizer pipe 157 is insulated from the electrolyzer to reduce current leakage. Alternatively, the brine tank 151 and the equalizer pipe 157 and the brine feed pipe 153 may be fabricated from fiberglass reinforced polymers such as polyesters, polyvinylidene chloride, and other polyhalocarbons.

It is to be understood that although the invention has been described with specific reference to particular embodiments thereof, it is not to be so limited since changes and alterations therein may be made which are within the full intended scope of this invention as defined by the appended claims.

We claim:

1. A bipolar electrolyzer comprising:

a plurality of individual electrolytic cells in series, each of said cells having an anolyte compartment and brine feed means, and said electrolyzer having an equalizer means independent of said brine feed means and comprising individual metal pipe means extending from openings in the anolyte compartments of the individual electrolytic cells to a common equalizer pipe means external the individual cells whereby to provide hydraulic communication between said anolyte compartments to maintain a substantially uniform head of anolyte in each of said cells.

2. The bipolar electrolyzer of claim 1 wherein the length of the individual metal pipe means and of the equalizer pipe means between adjacent cells is sufficient to provide an electrical resistance of from 5 to ohms when measured through sodium chloride brine contained in said individual pipe means and said 

1. BIPOLAR ELECROLYZER COMPRISING: A PLURALITY OF INDIVIDUAL ELECTROLYTIC CELLS IN SERIES, EACH OF SAID CELLS HAVING AN ANOLYTE COMPARTMENT AND BRINE FEED MEANS, AND SAID ELECTROLYZER HAVING AN EQUALIZER MEANS INDEPENDENT OF SAID BRINE FEED MEANS AND COMPRISING INDIVIDUAL METAL PIPE MEANS EXTENDING FROM OPENINGS IN THE ANOLYTE COMPARTMENTS OF THE INDIVIDUAL ELECTRLYTIC CELLS TO A COMMON EQUALIZER PIPE MEANS EXTERNAL THE INDIVIDUAL CELLS WHEREBY TO PROVIDE HYDRAULIC COMMUNICATION BETWEEN SAID ANOLYTE COMPARTMENTS TO MAINTAIN A SUBSTANTIALLY UNIFORM HEAD OF ANOLYTE IN EACH OF SAID CELLS.
 2. The bipolar electrolyzer of claim 1 wherein the length of the individual metal pipe means and of the equalizer pipe means between adjacent cells is sufficient to provide an electrical resistance of from 5 to 100 ohms when measured through sodium chloride brine contained in said individual pipe means and said equalizer piPe means. 